The present invention relates generally to a charging apparatus for introducing raw materials into a glass melting furnace and, more particularly, to socalled blanket batch chargers of the type disclosed in U.S. Pat. Nos. 3,780,889; 4,197,109 and U.S. Pat. No. 4,983,206, all commonly owned with the present application.
A continuous furnace used for the manufacture of glass typically comprises a large rectangular tank in which the molten bath of glass is contained. A raw batch mixture is continuously introduced into the furnace by batch charging apparatus of the type mentioned above. At the charging end of the furnace, the batch material is first melted in a melting zone, proceeds to a central zone, and then to a forehearth region where the molten glass is removed for formation into the desired finished product, such as flat glass or other shapes. The quality of the glass product is largely dependent upon the uniformity of the melt.
Furnace efficiency may vary considerably, depending upon the rate of batch feeding and the manner in which the raw batch material is introduced into the furnace. The charging end of the glass furnace typically includes a structure having a charging bay generally referred to in the art as the "doghouse". This furnace structure includes a suspended wall set inwardly from a lower rear wall of the charging bay, leaving an open or semiopen trough therebetween, defining the so-called doghouse across a substantial part of the full width of the furnace. This width varies, and in present furnace structures, can be on the order of 20 to 30 feet in width.
The doghouse provides a downwardly extending open area above the level of the molten glass into which the mixture of glass forming ingredients, or raw batch, is charged. The raw batch material initially floats on the molten glass and melts as it moves forward into the furnace. The batch charger disclosed in U.S. Pat. No. 4,983,206 has a charger plate that downwardly extends into the exposed area of the doghouse and reciprocates in a direction along the long axis of the furnace. The charger plate is positioned beneath a hopper chute such that as the charger plate moves forward from a retracted limit of travel, raw batch material from the hopper chute is deposited in a layer on the charger plate.
As the charger plate moves rearwardly, the layer of batch material then residing on the charger plate is obstructed by a seal device at the rear of the hopper from being carried rearwardly and therefore a row or "log"0 of charge is moved off the charger plate to fall over the nose of the charger plate onto the bath in the open area of the furnace from which the previous charge has just been cleared. This reciprocating cycle may be continuously repeated to maintain a substantially constant level of molten glass in the furnace as the melt is removed at the forehearth region.
Depending upon the rate of reciprocation, the nose or forward edge of the charger plate, just prior to depositing a new "log" of charge on the bath, may push a previously deposited "log" floating on the bath toward or under the suspended wall at the end of the doghouse into the melting zone of the furnace.
It has been observed that continuous melting furnaces of identical construction may exhibit unpredictable variations in performance due to eddy currents, convective currents, flame flow and other factors which influence the quality of the glass and fuel consumption or efficiency in the furnace. It has also been observed that a change in the feeding of the batch material results in a noticeable change in fuel efficiency. Because of the individuality of each furnace and the drift in melting conditions over periods of time, it is often necessary to adjust the batch feeder characteristics from time to time to improve furnace performance.
The final glass quality is dependent upon the quantity and placement of the raw batch material charged into the furnace with each reciprocating stroke of the charger plate. The adjustment of the stroke, while facilitated by the invention set forth in U.S. Pat. No. 4,983,206, is not an adjustment that can be made without discontinuing reciprocation for some short period of time.
It is thus desirable to be able to position the raw material logs as they are laid down on the top of the batch beyond the positioning that was available by simply adjusting the length of the stroke of the charger plates as with prior batch chargers of this type.